1. Field of the Invention
The present invention relates to a polishing apparatus for polishing a substrate, such as a semiconductor wafer, by bringing the substrate into sliding contact with a polishing pad, and more particularly to a polishing apparatus having a mechanism for regulating a surface temperature of the polishing pad.
2. Description of the Related Art
CMP (Chemical Mechanical Polishing) apparatus is used in a process of polishing a surface of a substrate in semiconductor device fabrication. The CMP apparatus is designed to hold and rotate the substrate by a top ring and press the substrate against a polishing pad on a rotating polishing table to polish the surface of the substrate. During polishing, a polishing liquid (e.g., slurry) is supplied onto the polishing pad, so that the surface of the substrate is planarized by a chemical action of the polishing liquid and a mechanical action of abrasive grains contained in the polishing liquid.
A polishing rate of the substrate depends not only on a polishing load on the substrate against the polishing pad, but also on a surface temperature of the polishing pad. This is because the chemical action of the polishing liquid on the substrate depends on the temperature. Thus, it is important for the semiconductor device fabrication to maintain an optimum surface temperature of the polishing pad during substrate polishing in order to increase the polishing rate and keep it constant.
FIG. 13 is a schematic view of a pad temperature regulator for regulating the surface temperature of the polishing pad. This pad temperature regulator includes a pad contact element 100 that is placed in contact with a polishing pad 102. The polishing pad 102 is secured to an upper surface of a polishing table 101 and is rotated in a direction indicated by arrow together with the polishing table 101. Liquid flows through the pad contact element 100, so that the surface temperature of the polishing pad 102 is regulated by heat exchange between the liquid and the polishing pad 102.
FIG. 14 is a perspective view of the pad contact element 100 shown in FIG. 13. The pad contact element 100 includes a passage-forming member 90 having a liquid passage formed therein and a cover member 91 secured to the passage-forming member 90. The cover member 91 has a liquid inlet 93 and a liquid outlet 94. The cover member 91 is fixed to an upper portion of the passage-forming member 90 by a plurality of bolts 92. The cover member 91 is made of PVC (polyvinyl chloride), and the passage-forming member 90 is made of sintered SiC (sintered silicon carbide).
FIG. 15 is a plan view of the passage-forming member 90 shown in FIG. 14, and FIG. 16 is a cross-sectional view taken along line A-A shown in FIG. 14. A partition 95 is provided in the passage-forming member 90, and a liquid passage 99 is formed on both sides of the partition 95. A temperature-controlled liquid is introduced into the pad contact element 100 through the liquid inlet 93, flows through the liquid passage 99 in direction indicated by arrow shown in FIG. 15, and is discharged from the pad contact element 100 through the liquid outlet 94. The surface of the polishing pad 102 is maintained at a predetermined target temperature by the heat exchange between the liquid flowing through the pad contact element 100 and the polishing pad 102.